1. Field of the Invention
The present invention relates to portable communication equipment that utilize retractable antennas. More particularly, the present invention relatesp 2 More particularly antenna for portable communication equipment that provides performance for the selected mode, retracted or extended, independent of the other mode.
2. Problems in the Art
Generally speaking, there are six related designs commonly used in the field of retractable antennas. Perhaps the simplest design is the fixed length linear whip radiator that has an electrical contact on one end, which makes contact with an electrical connector when the radiator is pulled out of the electronic device. In such a design, retraction of the radiator is accomplished by pushing the whip radiator downwardly from its connection with the connector and into the electronic device.
A further design in the prior art is the telescopic whip that is used for portable consumer products. The telescopic whip generally consists of progressively smaller diameter tubes that fit within the next tube. Such a technique permits the antenna to be collapsed or retracted to a length only slightly longer than the largest diameter tube.
U.S. Pat. No. 4,868,576 discloses a third type of design that consists of a linear whip radiator that is air-coupled to a monofilar helical matching device in the extended position. In the retracted mode, the monofilar matching helical device is used as the electromagnetic radiator.
U.S. Pat. No. 5,204,687 discloses yet another type of retractable antenna. U.S. Pat. No. 5,204,687 describes the retractable antenna as being a 1/4 wavelength retractable antenna that consists of a thin linear radiator having an isolated, short monofilar helical radiator on the end thereof. In the extended mode of operation, the thin linear radiator functions as a whip radiator having approximately a 1/4 wavelength electrical length. The helical radiator section is positioned on the upper end of the linear radiator and is isolated therefrom by a short section of dielectric preventing the helical radiator from being in the electrical circuit when the antenna is extended. When the antenna is in the retracted mode, the helical radiator is in the electrical circuit due to the retraction of the linear radiator into the electronic device with the helical radiator's electrical connection being made by a short metal tube below the helical radiator.
Yet another type of retractable antenna is that manufactured by Centurion International that consists of a 1/2 wavelength thin linear radiator with a short monofilar helical radiator connected to the end thereof. In either mode of operation, retracted and extended, the entire antenna package is in the electrical circuit.